\begin{problem}{Jealous Numbers}{jealous.in}{jealous.out}{1 second}{256 mb}

% Original idea : Andrew Stankevich
% Text          : Andrew Stankevich
% Tests         : Andrew Stankevich

There is a trouble in Numberland, prime number $p$ is jealous of another prime number $q$.
She thinks that there are more integer numbers between $a$ and $b$, inclusively, that
are divisible by greater power of $q$ than that of $p$.
Help $p$ to get rid of her feelings. 

Let $\alpha(n, x)$ be maximal $k$ such that $n$ is
divisible by $x^k$. Let us say that a number $n$ is $p$-dominating over~$q$ if
$\alpha(n, p)>\alpha(n, q)$.
Find out for how many numbers between $a$ and $b$, inclusive
are $p$-dominating over~$q$.

\InputFile

The first line of the input file contains $a$, $b$, $p$ and $q$ 
($1 \le a \le b \le 10^{18}$; $2 \le p, q \le 10^9$; $p \ne q$; $p$ and $q$ are prime).

\OutputFile

Output one number --- how many numbers $n$ between $a$ and $b$, inclusive,
are $p$-dominating over $q$.

\Example
\begin{example}
\exmp{
1 20 3 2
}{
4
}%
\end{example}

\bigskip

In the given example 3, 9, 15 and 18 are 3-dominating over 2.

\end{problem}
